1. Field of the Invention
The present invention is a process for improving the yields in a process for forming alkyl vanadates by the reaction of vanadium pentoxide and an alkyl alcohol in the presence of an azeotroping solvent.
2. Description of the Prior Art
Alkyl vanadates, which are useful as catalysts, can be formed by the reaction of vanadium pentoxide and an alkyl alcohol with by-product water being removed by an azeotroping solvent to help drive the reaction to completion. For example, benzene has been suggested for use as an azeotroping solvent in Bull. Acad. Sci. U.S.S.R. 1959, pp. 899-900 and in U.S. Pat. No. 3,920,751 to P. Charbardes et al. (Examples 5-6). Also suggested as a suitable azeotroping solvent is toluene (U.S. Pat. No. 3,657,295 to D. R. McCoy). More recently, alkane azeotroping solvents have been suggested (W. Magee, U.S. Ser. No. 245,868, filed Mar. 20, 1981).
Other methods for removing by-product water have been suggested to the exclusion of using an azeotroping solvent. In U.S. Pat. No. 3,987,074 to R. Haase et al., for example, the reaction of vanadium pentoxide and alkyl alcohol is conducted in the presence of an orthoester of the formula RC(OR').sub.3, where R is hydrogen or C.sub.1 -C.sub.5, and R' are each independently C.sub.1 -C.sub.12 or phenyl. In the Haase patent it is mentioned that prior art attempts to use strongly acidic catalysts promote the reduction of pentavalent vanadium to tetravalent vanadium and that such a side reaction is not desired. The Haase et al. process is described as one in which any unreacted vanadium pentoxide contains tetravalent vanadium on "only a negligible scale" so that it is not necessary to regenerate the pentoxide after each batch.